1. Field of the Invention
The present invention relates to a method for regenerating a carrier coated with a silicone resin or a resin containing a silane coupling agent in a spent electrophotographic developer which has been fatigued from continuous use in a copying machine, printer, etc. and to an electrophotographic developer containing the regenerated carrier.
2. Description of the Related Art
A two-component dry developer used for developing an electrostatic latent image in electrophotography comprises a toner and a carrier. The carrier is mixed and agitated with the toner in a development box to give a desired charge quantity to the toner and carries the charged toner onto an electrostatic latent image formed on a photoreceptor to form a toner image.
The carrier remains on the magnet of the development box and is returned to the development box where it is again mixed and agitated with fresh toner particles for repeated use.
In order to maintain high image quality over a service life of a developer in a stable manner, the carrier is required to have stable characteristics over the life.
Many of the state-of-the-art carriers for two-component dry developers for electrostatic latent image development have a resin coat for obtaining high image quality.
Because a developer is always under the stress of collisions among the particles or with the wall of a development box or a photoreceptor, etc. during the service life, the toner adheres to the surface of the carrier particles due to the heat generated by the collisions (called spent-toner phenomenon). Further, the resin coat falls off the carrier particles or undergoes denaturation, and the carrier characteristics are deteriorated with time, and it eventually comes necessary to exchange the developer for a new one.
In order to prevent deterioration of carrier characteristics, studies have been made on the resin to be used to coat the surface of a carrier. Of various resins proposed to date a silicone resin having a low surface tension has now been prevailing. However, the conventional silicone resins are still insufficient for preventing the spent-toner phenomenon or deterioration (fall-off and denaturation) of the resin coat.
A developer exchanged due to deterioration has been disposed as waste. However, environmental pollution by industrial waste has given a rise to a social problem, and it has been a subject to reuse the collected developer.
Proposals on reuse of a collected developer, especially a carrier, are disclosed, e.g., in Japanese Patent Laid-Open Nos. 89254/91, 149132/94, and 28280/95. These proposals aim at removal of the spent toner component adhered on the carrier surface but not at removal of the resin coat. Therefore, the resin remains on the regenerated carrier. Since the resin remaining on the carrier surface has undergone not a little deterioration (fall-off or denaturation) as a result of long-term use, the regenerated carrier shows instability in performance, failing to restore various initial characteristics such as electrical resistance and charging properties, or the regenerated carrier has reduced durability.
It has also been proposed to remove both a spent toner and a resin coat by heat treatment or organic solvent treatment as disclosed in Japanese Patent Laid-Open Nos. 12286/72, 212945/88, and 72665/95. However, these techniques, while effective on carriers coated with a styrene-acrylic resin or a like resin, are ineffective on carriers coated with a silicone resin or a resin containing a silane coupling agent because such a resin coat leaves SiO.sub.2 on the carrier surface when heat treated or the resin coat is insoluble in an organic solvent.